Hydrophilic silicone elastomers known so far are prepared by grafting of hydrophilic monomers directly on the surface or in the bulk of silicone elastomers as it is described by B. D. Ratner and A. S. Hoffman in "Radiation grafted hydrogels on silicon rubber as new biomaterials" in the book "Biomedical Applications of Polymers" (H. P. Gregor, ed.), Plenum Publishing Corp., New York. In this way, a homogenous hydrogel--silicon rubber material is obtained. However, the grafting was successful only with the mixture of N-vinylpyrrolidone and 2-hydroxyethyl methacrylate (HEMA), whereas HEMA alone gave only a surface grafted silicone rubber. Highest grafting was attained in an aqueous medium first if N-vinylpyrrolidone exceeded HEMA in volume. This homogeneous grafting changes the suitable properties of silicone rubber in the undesirable way.
Moreover, it is known that the plasticized PVC or also synthetic butadiene--acrylonitrile rubber may be filled with powdered synthetic hydrogels, as synthetic ion exchangers or relatively high crosslinked poly(2-hydroxyethyl methacrylate) (poly-HEMA), in the production of thin-walled articles, e.g. artificial leathers or impregnated fabrics. The reason and the result of the addition of powdered hydrophilic polymers was the enhanced permeability of water vapour in these polymers; see, for example, U.S. Pat. Nos. 3,875.261 and 3,928.704 (V. Heidingsfeld et al.). U.S. Pat. No. 4,228.205 (S. Hedecek et al.). In contrast to the above mentioned grafted silicon elastomers, the materials based on plasticized PVC and synthetic rubber were not applicable for medical purposes but only in the production of shoes, gloves, and protective apparels.